Microphone environmental protection device

REFERENCE TO RELATED APPLICATIONS

0001This is a continuation patent application of copending application Ser. No. 13/796,579, filed Mar. 12, 2013, entitled “Microphone Environmental Protection Device”, which claimed benefit under 35 USC §119(e) of provisional application No. 61/751,527, filed Jan. 11, 2013, entitled “Microphone Environmental Protection Device”. The aforementioned applications are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

0002Field of the Invention

0003This invention relates to devices used to protect microphones from the ambient environment.

0004Description of Related Art

0005Microphone screens typically incorporate porous materials, such as foamed material and metal mesh, to protect the microphone sensing surface, such as a diaphragm from being damaged by objects, such as fingers, and to prevent wind noise. Inventions such as those described in U.S. Pat. No. 7,496,208, U.S. Pat. No. 2,520,706 and U.S. Pat. No. 3,154,171 illustrate such examples.

0006However, there are significant problems with using porous materials such as foam. Foam and other similar porous materials become clogged with water when submerged or subject to rain. Porous materials absorb and hold water, dirt and salt crystals which change the nature of the sound sensed by the microphone. High frequency sounds are attenuated; therefore, the microphone signal no longer provides an accurate representation of sound in the ambient acoustic environment.

0007Microphones have inherent noise associated with them called “self-noise.” Even in a perfectly quiet ambient environment, microphones will generate electrical noise at their output. This noise is due to the self-noise of electrical amplifier components, such as the “Johnson noise” of resistances and “flicker noise” of transistors. The acoustical and mechanical damping of a microphone diaphragm also contributes to the self-noise of a microphone.

0008The “input referenced self-noise” (IRSN) of a microphone is the equivalent sound pressure level (SPL) that would generate the same noise at the electrical leads as the total effective self-noise of the microphone. The IRSN is typically described as an A-weighted value with units of decibels sound pressure level, or dB SPL, which is a weighted average over a frequency band. However, the IRSN may also be described as a dB SPL value at a single frequency.

0009Microphones with high self-noise can mask data, such as speech or music, when the data is at low levels. All other parameters being equal, microphones with lower self-noise are superior to microphones with higher self-noise.

SUMMARY OF THE INVENTION

0010The present invention protects a microphone from rain, wind, dirt, salt crystals and objects using a chamber having a perforated barrier. Fingers, vegetation, equipment and other objects are kept from contacting and damaging the microphone sensing surface, and a line of sight path from the ambient environment to the microphone is prevented, so that small particles such as sand and dust, water and wind do not impact directly on the microphone sensing surface or on an acoustic vent used to provide a waterproof barrier for the microphone. This provides improved damage protection.

0011Acoustic amplification of sound may be provided, which can result in an improvement of the signal-to-noise ratio of the microphone output signal.

0012In one embodiment, the invention can be attached to a noise-defending headset ear cup. In this embodiment the microphone is used to sense the sound outside of the ear cup and the microphone signal is input to an electronic processing circuit that is used to shape the signal and provide amplification and/or attenuation of the signal. The processing circuit signal output is input to an amplifier that is connected to a speaker to generate sound in the ear cup. In this way, the user can monitor ambient sounds and modify the amplitude and frequency content of the sounds to suit his/her needs. An embodiment of the invention may also be incorporated in manikins or other mechanical structures used to mimic the diffraction of sound around the human head.

BRIEF DESCRIPTION OF THE DRAWING

<figref idref="DRAWINGS">FIG. 1</figref> is a view of an embodiment of the invention as it would be incorporated into a vertical outer surface.

<figref idref="DRAWINGS">FIG. 2</figref> is a view of the interior of an embodiment of the invention with the perforated cover, screen and screws removed.

<figref idref="DRAWINGS">FIG. 3</figref> is a cross-sectional view of an embodiment of the invention along cut line B-B from <figref idref="DRAWINGS">FIG. 1</figref>.

<figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view of an embodiment of the invention along cut line A-A from <figref idref="DRAWINGS">FIG. 1</figref>.

<figref idref="DRAWINGS">FIG. 5</figref> is a view of an embodiment of the invention using slot perforations as it could be incorporated in an ear cup of a headset.

<figref idref="DRAWINGS">FIG. 6</figref> is a view of an embodiment of the invention using circular perforations as it could be incorporated in an ear cup of a headset.

<figref idref="DRAWINGS">FIG. 7</figref> is a view of an embodiment of the invention using a single slot perforation as it could be incorporated in an ear cup from a headset.

<figref idref="DRAWINGS">FIG. 8</figref> is a plot of the improvement in acoustic response when an embodiment of the invention with slot perforations is incorporated in an ear cup of a headset.

<figref idref="DRAWINGS">FIG. 9</figref> is a cross-sectional view of an embodiment of the invention along cut line C-C from <figref idref="DRAWINGS">FIG. 7</figref>.

<figref idref="DRAWINGS">FIG. 10</figref> is a cross-sectional view of an embodiment of the invention incorporating an auxiliary wind screen and drain tube.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

0023An embodiment of the invention is a device for protecting microphones against environmental damage which incorporates a special perforated barrier on the outer surface of a chamber, which provides a line of sight from outside the chamber volume to inside the chamber volume. The cross-sectional area of the perforations are large enough that water can easily pass through the barrier and the barrier is self-cleaned with rain or can be cleaned deliberately with a spray bottle. An outer layer of the barrier can be made of a solid rigid material, such as plastic or metal, with slotted perforations backed by an inner layer of metal mesh material.

0024A drainage path can be provided for water and debris that accumulate in the chamber volume. The water drain may be a path back through the perforated barrier, or a separated dedicated drain path can be provided. This allows the device to be self-cleaning during rain and easily to clean using a spray bottle.

0025The barrier in this embodiment is a rigid perforated surface forming a chamber which creates an effective acoustic mass. The total volume of the chamber creates an effective acoustic compliance. The combination of these two elements in this embodiment of the invention creates an acoustic resonator that is preferably in the frequency range of 1 kHz to 20 kHz.

0026Microphones have electronic and acoustic self noise. If the sound sensed by the microphone is increased, the effective signal-to-noise ratio of the microphone increases and yields an effectively quieter microphone signal for the same ambient acoustic noise signal.

0027An equalizer circuit (active or passive) can be connected to the output of the microphone to attenuate the frequency region of boosted signal. Therefore, because the microphone signal is attenuated, the self-noise of the microphone is reduced. However, because the acoustic resonator amplifies the sound through acoustical means, the measured signal strength remains at the same amplitude. Therefore, the signal-to-noise ratio of the microphone output is increased by the resonator of an embodiment of the invention and the effective IRSN is reduced which yields a higher quality microphone.

0028The microphone is located in a position relative to the chamber where there is no direct line of sight from the ambient environment outside the chamber to the sensing surface of the microphone. It will be understood that as used herein the phrase “no direct line of sight” is intended to mean that the sensing surface is located outside of, or spaced apart from, any imaginary sight line passing from the environment through the chamber. In other words, it is the location and conformation of the chamber and its relationship to the sensing surface of the microphone which provides the lack of line-of-sight from the environment to the sensing surface, rather than the prior art arrangement of having the sensing surface facing the environment with only a physical barrier such as a solid or foam or cloth cover providing the protection between the sensing surface and the environment.

0029In this way, any wind, sand or rain that is blown into the chamber through the perforated barrier makes its first contact with the physical structure of the chamber, instead of the microphone sensing surface, which reduces the kinetic energy compared to an unobstructed path. This helps protect the microphone sensing surface, such as a diaphragm, which can be damaged by the force from direct impact of rain or objects. Microphones, such as condenser, MEMS, dynamic and piezoelectric employ various types of sensing surfaces, such as single and multiple diaphragms and piezoelectric solids among others.

0030The microphone used in an embodiment of the invention is preferably waterproof. However, an additional waterproof membrane, called an acoustic vent, can be incorporated to block the path to the microphone sensing surface to ensure that the microphone is not damaged by contact with water. Acoustic vents may be attached directly to the front face of a microphone or other locations, such as the end of a microphone coupler, which would provide a water tight seal between the ambient environment and the microphone sensing surface.

0031<figref idref="DRAWINGS">FIG. 1</figref> depicts a view of an embodiment of the invention as it would be incorporated into a vertical outer surface with “UP” indicating the direction of higher altitude. A perforated cover <b>2</b> is attached to an outer surface <b>10</b>, using flush-mounted screws <b>6</b>. Alternatively, screws may be fastened from behind the outer surface so that the screws cannot be seen from the perspective shown.

0032The perforated cover <b>2</b> incorporates at least one slot perforation <b>4</b> having a length u and a height v. In a preferred embodiment, slot perforations are rounded at the ends and do not have sharp edges to help minimize wind turbulence when wind blows across the outer surface <b>10</b>.

0033Behind the slot perforations, a screen <b>8</b> is attached to the back of the perforated cover <b>2</b>. The screen <b>8</b> is preferably made of wire and coated with an oleophobic coating that tends to repel oil and other fluids, although other coatings, such as hydrophobic coatings, may also be used that tend to repel water and other fluids. The screen <b>8</b> prevents objects longer than slot length u from passing lengthwise through the slots. Alternatively, the screen <b>8</b> can be attached to the front of the perforated cover <b>2</b> to improve wind noise reduction.

0034A drain output <b>12</b> is located near the bottom of the perforated cover <b>2</b>. The drain output <b>12</b> is incorporated to more easily allow water, dirt and debris to drain out of the interior of an embodiment of the invention. The screen <b>8</b> does not cover the drain output <b>12</b>, so that dirt and other particles that may pass through the screen <b>8</b> to exit the interior of an embodiment of the invention.

0035<figref idref="DRAWINGS">FIG. 2</figref> is a view of the interior <b>24</b> portion of an embodiment of the invention, with the perforated cover <b>2</b>, screen <b>8</b> and screws <b>6</b> removed. Screw holes <b>14</b> are provided to receive the screws <b>6</b> that secure the perforated cover <b>2</b>. A rectangular screen recess <b>16</b> is incorporated to provide room for the screen <b>8</b> when the perforated cover <b>2</b> is attached. Within the interior <b>24</b> there is a chamber <b>20</b> with average width f and average height d (averages are used here because the interior is irregular).

0036At the upper end of the interior <b>24</b> is located a microphone coupler <b>18</b> which is acoustically coupled to the chamber <b>20</b>. The coupler <b>18</b> is preferably made of elastomeric material such as molded silicone or other compliant material.

0037The chamber <b>20</b> is enclosed by the interior structure and elements of an embodiment of the invention such that if water enters the chamber through the slot perforations <b>4</b> or drain output <b>12</b>, the only path for water to drain from the chamber is through slot perforations <b>4</b> and drain output <b>12</b>.

0038Within the chamber <b>20</b> is a recessed drain channel <b>22</b> with width k. The recessed drain channel <b>22</b> could be located as shown in the figure, or, alternatively could be centered, relative to dimension f, within the chamber <b>20</b>. The drain channel <b>22</b> may incorporate other geometries, such as an “hour glass” design where the drain channel becomes restricted in the middle, relative to dimension d of chamber <b>20</b>, while having greater width at the top, where the microphone coupler <b>18</b> is located, and at the bottom, where the drain output <b>12</b> would be located. The “hour glass” design provides for larger diameter microphone couplers and drain diameters while minimizing the total chamber <b>20</b> volume.

0039<figref idref="DRAWINGS">FIG. 3</figref> is a cross-sectional view of an embodiment of the invention along the cut line B-B from <figref idref="DRAWINGS">FIG. 1</figref>, cut through the length u of one of the slots <b>4</b>. In this view of an embodiment of the invention, a portion of the chamber has a depth h while the drain channel <b>22</b> is recessed further by depth w. Preferably, depth h should be greater than 1 mm to facilitate water drainage and prevent water retention. The interior geometry may be curved instead of the sharp edges shown in <figref idref="DRAWINGS">FIG. 3</figref>.

0040The drain channel <b>22</b> provides for improved draining of water from the chamber <b>20</b> but also allows room for incorporating larger diameter microphones and microphone couplers <b>18</b> without increasing the total chamber <b>20</b> volume appreciably. The drain channel is shown to one side of the chamber <b>20</b> but could as well be centered relative to dimension f, or placed in other locations in the chamber <b>20</b>.

0041The microphone coupler <b>18</b> has a coupler sound channel <b>30</b> that couples sound to an acoustic vent <b>26</b>. The microphone coupler <b>18</b> in this embodiment is located in the drain channel <b>22</b> because it is larger in diameter compared to h.

0042A cross-sectional view of the slot perforation <b>4</b> can be seen in <figref idref="DRAWINGS">FIG. 3</figref> with smooth contoured surfaces, such as a contour surface <b>33</b> facing the ambient environment instead of sharp edges to minimize wind turbulence and acoustic wind noise. The screen <b>8</b> has a mesh spacing z and a screen diameter q when the screen <b>8</b> incorporates cylindrical webbing such as metal wire and is shown here attached to the back of the perforated cover <b>2</b> to protect the screen <b>8</b> from damage. Alternatively, the screen <b>8</b> can be attached to the front of the perforated cover <b>2</b> for improved wind noise reduction.

0043The perforated cover <b>2</b> is attached to an enclosure <b>32</b>. The perforated cover <b>2</b> and enclosure <b>32</b> define the chamber <b>20</b> volume. The enclosure <b>32</b> extends to form the outer surface <b>10</b> in this embodiment. In another embodiment, the enclosure could be a separate component from the outer surface that attaches to the outer surface.

0044<figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view of an embodiment of the invention along cut line A-A from <figref idref="DRAWINGS">FIG. 1</figref>, through the width v of the slots <b>4</b>. The slots <b>4</b> have a thickness c measured between inner edge <b>47</b> and outer surface <b>51</b>.

0045Wind turbulence causes undesirable acoustic noise. Preferably, the slots <b>4</b> have smooth outer surfaces <b>51</b> instead of sharp edges to reduce turbulence due to wind when wind blows across the perforated cover <b>2</b>. The slot <b>4</b> inner edges <b>47</b> do not cause appreciable turbulence because wind is not blowing over this edge. However, the inner edge <b>47</b> may be contoured in alternative embodiments.

0046This cross-sectional view shows the microphone coupler <b>18</b> with a horn-shaped coupler sound channel <b>30</b> (although other geometries may be used), attached to a microphone <b>40</b>. Alternatively, the microphone <b>40</b> can be completely or partially installed within the chamber <b>20</b> to minimize the length of the coupler sound channel <b>30</b>, or if desired the microphone coupler <b>18</b> can be eliminated altogether. In the preferred embodiment, the microphone coupler <b>18</b> provides a water tight seal around the microphone <b>40</b>.

0047The coupler sound channel <b>30</b> couples sound from the chamber <b>20</b> to the acoustic vent <b>26</b>. The acoustic vent <b>26</b> is gas permeable and couples sound to the microphone <b>40</b>. The acoustic vent <b>26</b> is used to prevent water and dirt from impinging on a microphone sensing surface <b>42</b>, such as a fragile diaphragm. Preferably, the acoustic vent <b>26</b> is mounted to the microphone <b>40</b> with an adhesive <b>44</b> to cover a microphone inlet <b>46</b> and creates a water-tight seal.

0048As used herein, a “microphone inlet” is a perforation in a microphone housing to allow sound to be coupled to a microphone sensing surface from outside the microphone housing to inside the microphone housing. A “microphone sensing surface”, such as a diaphragm, typically vibrates in response to sound excitation, and this vibration is converted into an electrical signal using various means known in the art.

0049Sound impinging on the exterior of the perforated cover <b>2</b> passes through the slots <b>4</b> and screen <b>8</b> and into the chamber <b>20</b>, then through coupler inlet <b>48</b>, coupler sound channel <b>30</b>, acoustic vent <b>26</b> and microphone inlet <b>46</b>, where it is sensed by the microphone sensing surface <b>42</b>.

0050The slotted perforated cover <b>2</b> helps protect the acoustic vent <b>26</b> from rain, wind and sand as well as fingers and other foreign objects. Water that penetrates the perforated cover <b>2</b> runs down the chamber <b>20</b> and back out through the bottom slot perforations <b>4</b> and drain output <b>12</b>. The screen <b>8</b> prevents objects smaller than the slot dimensions u and v from entering the chamber <b>20</b>. Objects smaller than the mesh spacing z of screen <b>8</b> can enter the chamber <b>20</b>; however, they tend to fall to the bottom of the chamber <b>20</b>.

0051The drain output <b>12</b> has diameter k that is larger than the mesh spacing z so that small objects the size of the mesh spacing z can exit the chamber <b>20</b> easily without being trapped. The drain output <b>12</b> is located at the bottom of the chamber <b>20</b> so that gravity tends to pull water out of the chamber <b>20</b> via the drain output <b>12</b>. Thus, if any objects smaller than mesh z do enter the chamber <b>20</b>, water will wash the objects out of the chamber <b>20</b> through the drain output <b>12</b>. In this way, an embodiment of the invention tends to be self-cleaning.

0052When an embodiment of the invention is used near an environment where salt spray is present, salt crystals will not become trapped as they would if a porous foam material were incorporated. Any salt crystals that form from dried salt spray are also washed down the drain channel <b>22</b> during the next rain, and will exit through the drain output <b>12</b>.

0053The microphone <b>40</b> is located at the top of the chamber <b>20</b> so that any water which might enter the microphone area will fall out of the coupler sound channel <b>30</b> into the chamber <b>20</b> and exit out through the drain output <b>12</b>. Because there are no porous materials within the chamber <b>20</b> such as foam, water is not retained in the chamber <b>20</b>.

0054The microphone <b>40</b> is also located at a position outside of or spaced apart from any imaginary straight line from the ambient environment to the microphone sensing surface <b>42</b> or acoustic vent <b>26</b> (i.e there is “no line of sight”). That is, the microphone sensing surface <b>42</b> or acoustic vent <b>26</b> is obscured by the geometry of the microphone coupler <b>18</b>, the screen <b>8</b> and the slot perforations <b>4</b>. This is shown in <figref idref="DRAWINGS">FIG. 4</figref> as line of sight x. In this way, water spray and small objects cannot impact the microphone sensing surface <b>42</b> through a direct path. The acoustic vent <b>26</b> in this embodiment is also obscured and there is no line of sight from the environment to the vent <b>26</b>.

0055The acoustic vent <b>26</b> may be incorporated in other locations in an embodiment of the invention, such as at the coupler inlet <b>48</b>; however, care must be taken that there is no direct line of sight to the vent.

0056In the embodiment as shown in <figref idref="DRAWINGS">FIG. 4</figref>, there are multiple indirect unobscured lines of sight paths y from the ambient environment to the acoustic vent <b>26</b>. Materials, such as many acoustic foams, that do not have straight unobstructed paths through them tend to become clogged with water, dirt and salt crystals and need to be replaced regularly if they are used outdoors, whereas an embodiment of the invention described herein is self-cleaning and, if desired, can be deliberately cleaned by the user easily. In this embodiment, no material is used in the chamber <b>20</b>, and water easily drains from the chamber. However, highly porous material can also drain water adequately if there are unobstructed paths through the material, for water draining purposes, and the pores are relatively large in size.

0057A microphone amplifier <b>36</b> is connected to microphone leads <b>38</b> to provide bias circuitry and amplification. A passive or active electronic equalization circuit <b>34</b> can be connected to the microphone amplifier <b>36</b> to create a generally flat frequency response to ambient sound for sound recording or other purposes.

0058The perforated cover <b>2</b> and screen <b>8</b> are designed so that the acoustic mass of the two, combined with the acoustic compliance of the chamber <b>20</b>, form a first acoustic resonance at a frequency between 1 kHz and 20 kHz. The acoustic resonance amplifies the sound pressure in the chamber <b>20</b>, as compared to the ambient environment at and near the resonance frequency. Boosting the sound pressure has the desired result of improving the effective IRSN of the microphone <b>40</b>.

0059The acoustic compliance of the chamber <b>20</b> at room temperature is calculated using the equation C_a=(Vol/1.42×10⁵) m⁵/N, where Vol is the total volume of the chamber <b>20</b> in cubic meters (m³), m stands for meters and N stands for Newtons. The value of Vol is calculated using the equation Vol=edf m³, where e, d and fare the dimensions of the chamber <b>20</b> (see <figref idref="DRAWINGS">FIGS. 2 and 4</figref>), measured in meters.

0060Dimensions of 20 mm for d, 5 mm for e and 18 mm for f are an example of a desirable geometry which yields a volume of 1.8 cc, and an acoustic compliance of 1.27×10⁻¹¹m⁵/N. An average chamber depth e of greater than 1 mm is desirable to prevent water from becoming trapped within the chamber volume, and a slot width v of greater than 0.5 mm is desirable to prevent water from becoming trapped in the slots.

0061The acoustic mass of the perforated cover <b>2</b> and screen <b>8</b> will be dominated by the perforated cover <b>2</b> when the mesh diameter is small compared to the slot thickness c, and the mesh spacing z is similar in size to the slot width v.

0062The acoustic mass M_aof an individual slot or hole in kg/m⁴is approximated by the formula M_a=1.21 L/Area (ignoring end effects), where L is the thickness of the slots in meters, Area is the cross sectional area of the slots in square meters and Kg represents kilograms.

0063An example of desirable dimensions for slot <b>4</b> would be 2 mm for the thickness c, and 18 mm for the length u and 1.5 mm for the width v, where c is the thickness, and there are four slots. The diameter of the wires of screen <b>8</b> mesh in this embodiment is preferably 0.4 mm while the mesh spacing z is 0.8 mm.

0064Hence, the acoustic mass of a single slot of this geometry would be approximated as 90 Kg/m⁴. The equivalent acoustic mass of a plurality of slots of like geometry is equal to the acoustic mass of one slot divided by the number of slots. Hence, the acoustic mass in this preferred embodiment would be approximated as 22.5 Kg/m⁴.

0065The acoustic resonance frequency of the resonator in Hertz (Hz) can be calculated by the formula:

0066<maths id="MATH-US-00001" num="00001"><math overflow="scroll"><mrow><msub><mi>f</mi><mn>0</mn></msub><mo>=</mo><mfrac><mn>1</mn><mrow><mo>(</mo><mrow><mn>6.28</mn><mo>⁢</mo><msqrt><mrow><msub><mi>C</mi><mi>a</mi></msub><mo>⁢</mo><msub><mi>M</mi><mi>a</mi></msub></mrow></msqrt></mrow><mo>)</mo></mrow></mfrac></mrow></math></maths>

0067Using the values calculated above, the approximate resonance frequency is 9,400 Hertz (9.4 kHz). However, end effects of the slots and the screen result in higher acoustic mass due to the effective mass of the radiation impedance from the slots <b>4</b> and the acoustic mass of the screen <b>8</b>. End effects must be taken into account when the thickness of the slot is not large compared to the square root of the slot area and the calculations become complicated for slots when the wavelength of the sound is not large compared to the slot length. The end effects also are affected by how much edge contouring the designer uses for the slots.

0068Measurements of end effects for this geometry with a screen have been made in the Red Tail Hawk Corporation laboratory and yield an effective acoustic mass approximately four times as high as the calculated acoustic mass. Hence, the resulting resonance frequency is approximately 4.7 kHz for the design of this embodiment, rather than the calculated 9.4 kHz.

0069In the preferred embodiment, the chamber <b>20</b> volume Vol is less than 2.32 cc, so that a larger perforated area is not needed in the perforated cover <b>2</b> to achieve higher resonance frequencies. A smaller sized perforated area is easier to incorporate in devices such as headsets with earcups that have limited space available.

0070An acoustic device is considered in the “lumped-element” region when all its dimensions are small relative to the acoustic wavelength in question. A device with resonance frequency below 1 kHz will tend to attenuate high frequencies if the slot or hole perforations are much smaller than a wavelength and the system acts as a lumped-element system at higher frequencies. However, designs with resonances between 1 kHz and 20 kHz will transition out of the lumped-element region and will not attenuate high frequencies so long as the length of the slots is not small in relation to the wavelength of the sound wave.

0071The wavelength of a sound wave can be calculated as

0072<maths id="MATH-US-00002" num="00002"><math overflow="scroll"><mrow><mi>λ</mi><mo>=</mo><mfrac><mi>s</mi><mi>f</mi></mfrac></mrow></math></maths><br /> where λ is the wavelength in meters, s is the speed of sound (343 m/sec) and f is the frequency in Hz. A slot of length of 1.8 cm corresponds to a wavelength of 19 kHz. However, the behavior of the slot begins to transition out of the lumped element region at around 1.9 kHz.

0073Acoustic systems that have geometries both small relative to the wavelengths of the acoustic wave and roughly equal to or greater than the size of the acoustic wave are difficult to analyze with simple math and depend on the angle of acoustic wave incidence. A design, such as the design of this embodiment, must be measured in the laboratory and tweaked to achieve the desired results.

0074<figref idref="DRAWINGS">FIG. 5</figref> shows an embodiment of the invention as it can be incorporated into one of the two ear cups <b>64</b> of a headset (not shown). A second ear cup (not shown), generally similar in geometry to the ear cup <b>64</b> shown, is typically employed in headsets, with the two earcups coupled by a headband (not shown) attached to both ear cups. Headband attachments <b>66</b> are provided on the ear cup <b>64</b> to mechanically attach a headband to the ear cup <b>64</b>.

0075In this embodiment of an embodiment of the invention, a perforated cover <b>62</b> is attached to an outer surface <b>60</b> of the earcup, typically using screws (not shown) attached from inside the ear cup <b>64</b>. In this way, the screw heads cannot be seen from outside the ear cup <b>64</b>. The enclosure of an embodiment of the invention in this embodiment also forms the outer surface <b>60</b> of the ear cup <b>64</b>. The perforated cover <b>62</b> follows the contour of the outer surface <b>60</b> of the ear cup <b>64</b> to minimize wind turbulence and wind noise. The perforated cover <b>62</b> employs slot perforations <b>76</b> a screen <b>72</b> attached to the front of the perforated cover <b>62</b> and a drain output <b>70</b>. When worn on the head, the drain output <b>70</b> is located below the perforated slots <b>76</b> to facilitate water drainage. The drain output <b>70</b> in this embodiment is located on the perforated cover <b>62</b>. The screen <b>72</b> does not cover the drain in this embodiment.

0076A partition can be employed behind the enclosure of an embodiment of the invention and within the ear cup to seal an embodiment of the invention and all related circuitry to achieve a waterproof design. In this way, if the headset is submerged in water, no water will penetrate into the partitioned volume. When an embodiment of the invention is incorporated in the ear cup of a headset and the headset is used in wet conditions or submerged, no water damage is caused to the microphone or electronics, and because water drains from the chamber of an embodiment of the invention quickly, normal microphone function is restored once the headset is removed from the water.

0077<figref idref="DRAWINGS">FIG. 6</figref> shows another embodiment of an embodiment of the invention as it can be incorporated into one of the two ear cups <b>64</b> of a headset (not shown). Circle perforations <b>80</b> are employed instead of slot perforations in this embodiment. A perforated cover <b>78</b> is attached to the outer surface <b>60</b> of the ear cup <b>64</b> using flush-mounted screws <b>76</b>. A screen is not employed, nor is a drain output in this embodiment. Water drains from the circle perforations <b>80</b> if an embodiment of the invention gets wet.

0078<figref idref="DRAWINGS">FIG. 7</figref> shows another embodiment of an embodiment of the invention as it can be incorporated into one of the two ear cups <b>84</b> of a headset (not shown). <figref idref="DRAWINGS">FIG. 9</figref> shows a sectional view of the embodiment, cut through lines C-C in <figref idref="DRAWINGS">FIG. 7</figref>.

0079In this embodiment, only a single slot perforation <b>86</b> is employed. The perforated cover in this embodiment is molded into the ear cup <b>84</b> body itself. The earcup provides an outer surface <b>82</b>. The enclosure of an embodiment of the invention in this embodiment is a separate component that is attached to the ear cup from inside the ear cup using screws, adhesive, ultrasonic welding or other means. A screen <b>76</b> is employed to keep larger objects from penetrating into the chamber of an embodiment of the invention. Water drains through the single slot perforation <b>86</b> and screen <b>76</b>.

0080<figref idref="DRAWINGS">FIG. 9</figref> is a cross-sectional view of an embodiment of the invention along cut line C-C from <figref idref="DRAWINGS">FIG. 7</figref>, through the slot <b>86</b>. In this embodiment the microphone coupler <b>90</b> incorporates a coupler sound channel <b>92</b> that is short and cylindrical in geometry, and the microphone coupler <b>90</b> is not much bigger than the microphone <b>40</b> in overall size. No acoustic vent is employed in this embodiment, and the chamber <b>94</b> in this embodiment does not incorporate a recessed drain channel. There is no line of sight from the ambient environment to the microphone sensing surface <b>42</b> which helps protect the microphone sensing surface <b>42</b> from the direct impact of blowing rain, sand and other objects. (For example, sighting along ray trace xx one cannot see the microphone sensing surface <b>42</b>.) In this embodiment, the microphone <b>40</b> used does not suffer from detrimental effects from exposure to water (waterproof design). If a non-waterproof design were incorporated in this embodiment, an acoustic vent <b>26</b> would be used as a water bather for the microphone <b>40</b>, for example, as shown in <figref idref="DRAWINGS">FIG. 3</figref> and <figref idref="DRAWINGS">FIG. 4</figref>. There is an indirect unobstructed line of sight yy from the ambient environment to the microphone sensing surface <b>42</b>. That is, there are no acoustic foams or other materials in the chamber <b>94</b> that would block a path from the ambient environment to the microphone sensing surface <b>42</b> and tend to retain water.

0081<figref idref="DRAWINGS">FIG. 10</figref> shows a cross-sectional view of an embodiment of the invention incorporating an auxiliary wind screen <b>97</b>, a drain tube <b>95</b> and a drain output <b>99</b>. The auxiliary wind screen <b>97</b> can be attached to the outer surface <b>82</b>. It may have a geometry that follows the contour of the outer surface <b>82</b> or may be bulbous or other geometries that reduce wind noise.

0082The auxiliary wind screen <b>97</b> can be constructed using mesh screen, cloth, gas-permeable membranes, foam or other materials that reduce wind noise but do not alter the acoustic audio-frequency sound sensed by microphone <b>40</b> in a detrimental way. The auxiliary wind screen <b>97</b> may be thin, for example when employing a single mesh screen or multiple mesh screen layers, or thick, for example when employing foam material with a hollow interior, or solid, for example when employing a solid piece of foam; other wind screen geometries may also be used.

0083The drain tube <b>95</b> is coupled to the chamber <b>94</b> and drain output <b>99</b> for draining debris, water and/or other fluids into the ambient environment. Alternatively, the drain tube <b>95</b> could drain to the interior environment, or other regions, instead of the ambient environment if desired.

0084<figref idref="DRAWINGS">FIG. 8</figref> shows a plot depicting the difference in the response of a microphone mounted flush on the outer surface of an ear cup compared to the response of a microphone used in an embodiment of the invention in an ear cup with four slot perforations and similar aforementioned dimensions, at a range of audio frequencies. That is, the plot in <figref idref="DRAWINGS">FIG. 8</figref> shows a graph of the improvement in microphone sensitivity when using an embodiment of the invention compared to flush-mounting the microphone.

0085The plot is an average of three measurements from three different incidence angles (front, side, back) for a plane pressure wave incident on the ear cup when placed on an acoustic manikin in an anechoic room. The response shows a gain in sensitivity in the frequency range from approximately 1 kHz to 8 kHz. In this frequency band, the signal-to-noise ratio has been improved by an embodiment of the invention because the self-noise of the microphone alone has not changed. The first resonance frequency of an embodiment of the invention in this embodiment is approximately 4.7 kHz. There are other resonances and antiresonances due to the headset geometry and invention above 4.7 kHz.

0086Although there are several higher-frequency ranges where the response is attenuated, there is a significant net gain in output sensitivity due to the resonance characteristics of an embodiment of the invention, which results in a significant net improvement in the IRSN.

0087Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.